This investigation examines the reactivity of phosphinoboronate esters Ph₂PBpin (pin = 1,2-O₂C₂Me₄) and Ph₂PBcat (cat = 1,2-O₂C₆H₄), as well as other phosphinoboron species, with various aryl and aliphatic acyl chlorides. These reactions proceed smoothly to give acyl phosphines of the type RC(O)PR′₂ along with loss of a boron-chloride compound. In some cases, a second equivalent of the phosphinoboron species can add to the CO double bond at elevated temperatures to give the corresponding diphosphines RC(OBR′′₂)(PR′₂)₂. These ambiphilic diphosphines behave like substituted (1,1-bis(diphenylphosphino)methane) derivatives in a reaction of PhC(OBpin)(PPh₂)₂ (2a) with (η⁵-C₉H₇)Rh(η²-coe)₂ (coe = cis-cyclooctene) affording the indenyl rhodium complex (η⁵-C₉H₇)Rh(PhC(OBpin)(PPh₂)₂) (3a) where the phosphines are bound to the metal centre in a κ²-P,P bidentate manner.